1. Field of the Invention
The present invention relates to light scanning devices, laser radar devices, and light scanning methods.
2. Description of the Related Art
There is a conventional laser radar device capable of monitoring a wide-angle visual zone in the front forward visual zone and side visual zone of the device. Such a laser radar device is mounted in general on a vehicle and transmits laser light toward the front forward visual zone and side visual zone of the vehicle in order to detect obstacles which are present in the front visual zone and size visual zone of the vehicle, and to detect the distance between the laser radar device (namely, the vehicle) and the target front obstacle.
The laser radar device is generally comprised of a light output unit and a light detection unit. The light output unit generates and transmits laser light. The light detection unit receives and detects the laser light reflected by the obstacles. It is necessary for the light output unit of the laser radar device to scan the wide-angle visual zone with a high resolution without generating any dead visual zone.
Such a type of the conventional light scanning device generally aligns polarized laser light and emits the aligned laser light to the scanning visual zone in order to uniformly scan the laser light to all directions in the scanning angle. Conventional patent documents, for example, Japanese patent laid open publications No. JP H09-021872, and No. JP H07-12569, have disclosed the conventional laser radar device.
The conventional scan-type distance detection device which is disclosed, for example, in JP H09-021872 has an improved function which expands the detection angle (or range) of the scanning visual zone, to which the laser light is scanned, without decreasing the resolution in the rotating direction of a scanning mirror by preventing the projection image in the entire scanning angle (or range) from being rotated and by rotating an image rotating prism which is linked together with the scanning mirror.
The conventional detection device disclosed in JP H07-12569 is capable of detecting a target object on the basis of the laser light which is reflected by the target object. This conventional detection device scans the laser light to the target detection zone. The laser light is polarized light which is limited in polarized direction in order to eliminate strong reflections from the laser light reflected by glossily flat surfaces.
However, when the scanned laser light has the same polarized direction in each of directions in the entire scanning angle in the wide-angle visual zone of the laser radar device mounted on a vehicle, the laser light reflected from both sides of the wide-angle visual zone has a decreased strength (or sensitivity). This would cause various problems.